This is a technology development proposal that will create a new technology base for cochlear electrodes. The goal is to produce a micro-machined, multi-contact electrode array using a biocompatible, bioresistant, dimensionally stable, polymer substrate Because this polymer substrate is dimensionally stable, thin metal traces can be micro-machined for electrode contacts and interconnects The resulting electrode array can be as thin as 25mm, less than 0 5mm wide and very flexible. With this small, flexible array as a beginning point, the mechanical aspects at every point along the length of the complete intra-cochlear implant can be specified and optimized. These mechanical characteristics of shape, springiness, and flexibility in two planes determine the probability of trauma during surgical insertion. Thus, an electrode with idealized mechanical properties will result in less trauma Benefits of this new technology would also include improved electrode positioning necessary for more efficient coupling to the residual neural elements, a larger number of electrode contacts and possibly deeper insertion into the lower frequency portions of the cochlea. Goals of Phase I are design and fabrication of several iterations of electrode carriers and electrode arrays, mechanical structuring of the arrays, and saline soak testing for electrical properties. In preparation for Phase II, an implantable integrated circuit diagnostic stimulator for detailed study of the assembly stability under realistic chronic implant conditions in-vitro and in-vivo will be developed. Phase II research will involve further optimization of the intracochlear electrode arrays based on results of extensive in-vivo measurements of performance using CNS recording paradigms at UCSF and analysis of insertion trauma in cat and human cadaver material. Long-term reliability of the technology will be evaluated in-vitro and in-vivo using the implantable diagnostic stimulator. An integrated circuit stimulator will be developed based on results of the diagnostic stimulator and embedded within the terminal portion of the polymer substrate. This new, robust, intracochlear implant will be useful for advanced chronic physiology studies and clinical application.